The present invention relates to a beer filtering device to be used in production of beer, and more particularly to a beer filtering device having a structure of a multi-stage filter press type, which is characterized in a washing and sterilizing function before or after a filtering step.
In general, the production of beer is roughly classified into the steps of (1) making malt from barley; (2) making wort from the malt; (3) fermenting the wort with yeast and ripening the wort to make a beer stock; and (4) filtering the beer stock to obtain the beer.
The filtering step is carried out by passing the ripened beer stock through a filtering device to thereby remove the yeast, bacteria, protein, etc. and obtain a transparent amber beer. If the yeast or the bacteria resides in the beer, a yeast odor is left in the beer, or the beer becomes cloudy and unstable. Particularly in case of producing a draft beer which is not subject to heat treatment, the bacteria or the like must be sufficiently removed by filtration. Thus, the filtering step as the final step of the production of beer is important, and such filtration is called precision filtration since it is performed by using a very fine filter element with a high precision.
It is known that various types of filtering devices are employed for the filtration of beer. For example, a filtering device of a multi-stage filter press type is employed for the filtration of beer. In such a filtering device, a plurality of filter elements are arranged side by side with a plurality of filter plates and filter frames, and the whole is pressed. The beer stock is supplied to the filter elements in parallel to be filtered, and the filtrate of the beer stock is recovered from each filter element in parallel.
More specifically, the filter elements are respectively supported to the filter plates, and a filter chamber is defined in each filter frame so as to face each filter element. The filter plates and the filter frames are arranged side by side in alternate relationship to each other to form an array. In filtering the beer stock, a pressure is applied from press means to the array of the filter plates and the filter frames sandwiched relative to each other.
A stock line for supplying the beer stock to the filter elements and a filtrate line for recovering the filtrate are independently formed through the array of the filter plates and the filter frames. The stock line is constituted of a plurality of stock line holes penetrating through the filter plates and the filter frames, and the filtrate line is constituted of a plurality of filtrate line holes penetrating through the filter plates and the filter frames. The adjacent ones of the stock line holes are adapted to be sealedly communicated with each other through a stock line seal, and the adjacent ones of the filtrate line holes are adapted to be sealedly communicated with each other through a filtrate line seal.
In the filtering step, when the pressure is applied from the press means to the array of the filter plates and the filter frames, the stock line seals and the filtrate line seals are brought into a sealing condition to thereby liquid-tightly seal the stock line and the filtrate line and define a filter chamber between the opposed filter plates through the filter frame. In this condition, the beer stock is supplied from the stock line to each filter element, and the filtrate from each filter element is collected to the filtrate line. Further, in case of maintenance such as replacement of the filter elements, the pressure of the press means is removed to move the filter plates and the filter frames away from each other and thereby cancel the sealing condition of the stock line seals and the filtrate line seals.
Each of the stock line seals and the filtrate line seals is mounted on an outer peripheral portion or a central portion of each filter plate or each filter frame, and it is made of an elastic material such as rubber.
Meanwhile, it is very important to wash and sterilize the interior of the filtering device before or after the filtering step. If such a washing step is not performed, the filtrate is contaminated by bacteria residing in the interior of the filtering device, so that the filtration becomes insignificant.
The washing step is simply performed by forcing a sterilizing washer liquid into the filtering device instead of the beer stock. Accordingly, in the washing step, the washer liquid flows in a sealed passage for the beer stock and a sealed passage for the filtrate to thereby wash and sterilize these sealed passages.
However, the washer liquid cannot be circulated through a pressure-contact surface of the filter element between the filter plate and the filter frame adjacent to each other and in the peripheries of the stock line seals and the filtrate line seals. As a result, there is a possibility that bacteria residing in the peripheries of these seals enter the sealed passages to contaminate the filtrate in the filtering step.